Conventionally, mold parts are made by machining and/or die casting metals. In this manufacture, where cooling passages are required, these may be formed by machining the passages through the parts. Alternatively, when the cooling passages are of complex form and shape, tubular heat exchange members are disposed in specific locations within the mold parts. This is achieved by disposing the tubular heat exchange members in specific positions and then die casting the mold parts around them. These procedures are extremely expensive; time consuming and labor intensive. They involve the intricate design of the mold parts, use of expensive metal cutting machinery for removal of unrequired metal and/or the design and manufacture of special die casting tools to perform the die casting operations required. Mold parts, because of their expense, are intended to have a long working life and their useful working life does in many cases far exceed their required working life. The expense directly reflects upon the production cost and sale price of the articles which are to be molded by the mold parts and much profit must be lost where only a portion of the useful working life of a mold part is actually required as when, for instance, manufacture of the molded articles is discontinued for any reason.
Apart from the expense, because of restrictions of manufacture, i.e. drilling or use of tubular members for the cooling passages, it is sometimes extremely difficult or even impossible to dispose these passages in most desirable locations within a mold in order to achieve the most efficient mold cooling. This may result in undesirable hot spots in a mold which will need design modifications to overcome or degradation in the molded plastic of the molded product may result.